The present invention relates to evaporative condensers for use in cooling systems; and more particularly to apparatus for controlling the treatment of water used in such condensers.
Large cooling systems, such as those found in commercial and industrial buildings, have an exterior evaporative condenser to remove heat from the building interior or from an industrial process. These evaporative condensers are commonly called "cooling towers." A pump circulates water from a reservoir at the base of the cooling tower through a shell or tube heat exchanger where the water picks up waste heat from a refrigeration system or industrial process. The water flows back to the cooling tower where it is sprayed into a stream of air that is drawn or forced through the cooling tower, thereby promoting evaporation of the water which removes heat from the system. Some of the water evaporates before it reaches the reservoir at the bottom of the cooling tower. When the water level in the reservoir drops below a given point, a level activated valve opens which introduces water from a supply to replace, or make-up for, the water which has evaporated.
As the water evaporates over the course of time, the concentration of minerals and other dissolved solids in the circulating water increases. Periodically, an outlet valve of the reservoir is opened to drain some of the water which has a high concentration of total dissolved solids. This water is replenished by water from the supply causing the concentration of dissolved solids in the cooling tower water to diminish. The draining process is commonly called a "bleed-off". Conventional systems for automatically controlling the bleed-off measure the electrical conductivity of the water and open the drain valve when the conductivity exceeds a threshold level which corresponds to an undesirably high concentration of total dissolved solids. Standard conductivity sensors become fouled with minerals over time which diminishes the accuracy of the sensor. Therefore, the sensors periodically must be tested and cleaned when their accuracy falls outside a tolerance range.
Because the cooling tower is open to the atmosphere, algae, bacteria and other organisms can exist and multiply within the reservoir. In response to a programmable time clock, biocides were added to the reservoir water to eliminate these organisms. The concentration of biocides diminishes as the water is drained from the reservoir and new water is added, thereby requiring periodic addition of more biocide.
The internal components of the cooling system may corrode over time depending upon the acidity of the water from the supply. To counter this effect, a corrosion inhibitor also is added to the cooling tower water and must be replenished in order to maintain the proper concentration as water is bled from the system. Previous systems for treating the cooling system water added corrosion inhibitor whenever the bleed-off control discharged water from the system. However, such conductivity based systems can apply more chemical than is required to adequately treat the water.
It is therefore desirable to provide an automatic control system for bleeding off the cooling tower when the concentration of total dissolved solids becomes excessive. The control system also should add the biocides and corrosion inhibitors as needed. However, in order to reduce operating expenses,, the addition of chemicals must be regulated so that only the amounts necessary for satisfactory operation are added to the cooling tower. It is also desirable that the accuracy of the system be periodically checked and an indication given to the operator when maintenance is required, such as cleaning the conductivity sensor.